Infrared sensor integrated in a touch panel

ABSTRACT

An infrared source is configured to illuminate the underside of one or more objects on or above a touchable surface of a touch panel. Infrared light reflected from the underside of the object(s) is detected by an infrared sensor integrated in the touch panel below the touchable surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 13/046,481 titled “INFRARED SENSOR INTEGRATED IN A TOUCH PANEL”which was filed on Mar. 11, 2011 and issued on Apr. 2, 2013 as U.S. Pat.No. 8,411,070, and which is a continuation of U.S. patent applicationSer. No. 11/604,491 titled “INFRARED SENSOR INTEGRATED IN A TOUCH PANEL”which was filed on Nov. 27, 2006 and issued on Apr. 12, 2011 as U.S.Pat. No. 7,924,272. These patent applications are expressly incorporatedherein by reference.

BACKGROUND

Systems having optical sensor arrays directly incorporated into a thinfilm transistor (TFT) liquid crystal display (LCD) have been proposed.Many different uses for such systems exist, for example, as a scanner,fingerprint sensor or touch screen. Such a system has two images: theimage displayed on the LCD display screen and the image detected by theoptical sensor array. Light from the display itself may add noise orambiguity to the image detected by the optical sensor array, if theoptical sensor array detects visible light in the same wavelengths asthat emitted by the display

In a shadow mode of operation, the sensor array may sense one or moreobjects such as a finger on or above the display screen by detecting theshadow of the ambient light cast by the object. The image from thesensor array is then processed to obtain the X,Y coordinates of theobject(s). A sensor array used in shadow detection may require a veryhigh dynamic range in order to detect shadows in ambient lighting theilluminance of which can vary over many orders of magnitude. If theambient lighting is too dark, there is no shadow, and the method failscompletely. Moreover, shadow detection is unable to detect patterns,designs, and other details on the object surface that is in shadow.

In a reflective mode of operation, a controlled light source is used toilluminate one or more objects such as a finger on or above the displayscreen. The backlight is a controlled light source, and by turning allpixels on in a color LCD, a uniform white light is transmitted throughthe display. The reflection of this light from the object(s) may bedetected by the optical sensor array and processed. However, if the LCDis displaying a black image, then the backlight is not illuminatinganything in the region above the image and any objects in that regionwill not be detected. An arbitrary image displayed on the LCD willaffect how much of the backlight is transmitted through the LCD andtherefore the illumination of objects on or above the display screen.Consequently, in reflective mode, an arbitrary image on the displayscreen may interfere with the detection of objects on or above thedisplay screen.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

An infrared source illuminates the underside of one or more objects onor above a touchable surface of a touch panel system. Infrared lightreflected from the underside of the object(s) is detected by an infraredsensor integrated in the touch panel. The output of several of suchinfrared sensors may be processed to identify a detected infrared image.The infrared sensors may be distributed throughout the touch panel, inparallel to the touchable surface. Since the image to be detected issensed in the infrared portion of the spectrum, it does not conflictwith any image displayed in the visible portion of the spectrum on adisplay incorporated into the touch panel.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not limitation in thefigures of the accompanying drawings, in which like reference numeralsindicate corresponding, analogous or similar elements, and in which:

FIG. 1 illustrates an exemplary interactive display system incorporatinga touch panel system;

FIGS. 2A, 2B and 2C illustrate cross-sections of exemplary touch panelsystems;

FIG. 3 illustrates a cross-section of an exemplary touch panel systemhaving an exemplary liquid crystal display incorporated therein;

FIG. 4 illustrates a cross-section of an exemplary touch panel systemhaving another exemplary liquid crystal display incorporated therein;

FIG. 5 illustrates a cross-section of an exemplary touch panel systemhaving yet another exemplary liquid crystal display incorporatedtherein;

FIG. 6 illustrates an exemplary active matrix circuit having a TFT-basedinfrared sensor integrated therein;

FIG. 7 is an example of a cross section of a bottom gateinfrared-sensitive TFT;

FIG. 8 illustrates an exemplary active matrix circuit having aphotodiode-based infrared sensor integrated therein; and

FIG. 9 illustrates a cross-section of an exemplary touch panel systemhaving an organic light emitting diode display incorporated therein;

FIG. 10 illustrates a cross-section of another exemplary touch panelsystem having an organic light emitting diode display incorporatedtherein;

FIG. 11 illustrates an exemplary active matrix organic light emittingdiode (OLED) circuit having a TFT-based infrared sensor integratedtherein; and

FIG. 12 illustrates an exemplary active matrix OLED circuit having aphotodiode-based infrared sensor integrated therein.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of embodiments of thedescribed technology. However it will be understood by those of ordinaryskill in the art that the embodiments may be practiced without thesespecific details. In other instances, well-known methods, procedures andcomponents have not been described in detail so as not to obscure theembodiments of the described technology.

A touch panel system according to the described technology may have manydifferent applications. For example, touch panels that have displaycapabilities may be used for interactive display. FIG. 1 illustrates anexemplary interactive display system incorporating a touch panel system.An interactive display system 100 comprises a touch panel system 102coupled to a computer 104. Computer 104 may be controlled via a monitor106 and a keyboard 108 or any other suitable user interface. Touch panelsystem 102 is thin and is generally placed on a flat surface, such asthe top of a table 110 or hanging from a wall. Touch panel system 102comprises a touch panel and has a touchable surface 112. The touch panelis also a display, and a graphic image 114 displayed by the display isviewable via touchable surface 112. In the example shown in FIG. 1, thegraphic image 114 is that of a maze. Computer 104 provides processingpower that yields a rich user interactive experience. As players movephysical game pieces 116 around the maze, touch panel system 102 is ableto detect the location of the game pieces, and to alter the displayedgraphic image accordingly. For example, the walls of the maze may bemoved to increase the complexity of the game, or a video clip may beshown if a game piece is placed on a certain location in the maze.

Infrared (IR) sources in system 102 illuminate the physical game pieces116. IR radiation reflected from game pieces 116 is detected by IRsensors that are integrated into the touch panel. Signals from the IRsensors are processed by computer 104 to identify the locations ofphysical game pieces 116 on touchable surface 112. Any suitable methodfor distinguishing between different game pieces 116 on touchablesurface 112 may be used. For example, physical game pieces 116 may havedistinct shapes or may have symbols such as bar codes imprinted on theirundersides. Since infrared radiation is used to detect the locations ofphysical game pieces, graphic image 114 does not affect the detection.Similarly, ambient visible light or lack thereof does not affect thedetection.

FIG. 2A illustrates a cross-section of an exemplary touch panel system.A touch panel system 200 comprises a touch panel 202 that has severalinfrared (IR) sensors 204 integrated therein. Objects above a touchablesurface 206 include an object 208A that is in contact with touchablesurface 206 and an object 208B that is close to but not in actualcontact with (“adjacent”) touchable surface 206. Infrared sensors 204are distributed throughout touch panel 202 parallel to touchable surface206. One of infrared sensors 204 may detect infrared radiation reflectedfrom objects 208A and 208B, as indicated by arrows 210. Although theterm “above” is used in this description, it should be understood thatthe orientation of the touch panel system is irrelevant. As shown inFIG. 2, touchable surface 206 is horizontal, but in a differentembodiment generated by rotating system 200 clockwise by 90 degrees,touchable surface 206 could be horizontal. In that embodiment, theobjects from which reflected IR radiation is detected are to the side oftouchable surface 206. The term “above” is intended to be applicable toall such orientations.

Touch panel 202 may comprise filters 212 that absorbs visible light andtransmits infrared radiation and are located between touchable surface206 and IR sensors 204 in order to shield IR sensors 204 from visiblelight 214 incident on touchable surface 206 in the case where IR sensors204 are sensitive to a broader range of wavelengths of light other thanpurely infrared wavelengths.

Touch panel 202 may comprise a display that is configured to displayimages that are viewable via touchable surface 206. An eye 215 indicatesa possible direction from which the images are viewed. The display maybe, for example, an LCD, an organic light emitting diode (OLED) display,a flexible display such as electronic paper, or any other suitabledisplay in which an IR sensor can be integrated.

System 200 may comprise a backlight 216 for the display. Backlight 216may comprise at least one IR source 218 that is configured to illuminateobjects in contact with or adjacent touchable surface 206 with infraredradiation through touchable surface 206, as indicated by arrows 220. IRsensor 204 s are only sensitive to radiation incident from above, so IRradiation traveling directly from backlight 216 to IR sensor 204 s isnot detected.

The output of IR sensors 204 may be processed to identify a detectedinfrared image. The IR radiation reflected from the objects may bereflected from reflective ink patterns on the objects, metal designs onthe objects or any other suitable reflector. For example, white paperreflects IR radiation and black ink absorbs IR radiation, so aconventional bar code on a surface of an object may be detected by aninfrared-sensing device according to the described technology. Fingersare estimated to reflect about 10% of the near IR, which is sufficientto detect that a finger or hand is located at a particular location onor adjacent the touchable surface. A higher resolution of IR sensors maybe used to scan objects to do applications such as document scanning andfingerprint recognition. For example, fingerprint recognition generallyrequires a resolution of more than 200 dots per inch (dpi).

FIG. 2B illustrates a cross section of another exemplary touch panelsystem. A touch panel system 250 comprises touch panel 202 havingseveral IR sensors 204 integrated therein, a frontlight 254 and abacklight 255. Backlight 255 does not comprise any IR sources, whereasfrontlight 254 comprises at least one IR source 258. Due to the presenceof frontlight 254, a touchable surface 256 of system 250 is actually asurface of frontlight 254 and not of touch panel 202. Infrared sensors204 are distributed throughout touch panel 202 parallel to touchablesurface 256. IR source 258 is configured to illuminate objects abovetouchable surface 256, for example, objects 208A and 208B, with IRradiation through touchable surface 256. Frontlight 254 may comprise alight guide (not shown), so that IR radiation emitted from IR source 258travels through the light guide and is directed towards touchablesurface 256, as indicated by dashed lines 260.

In other touch panel systems, both the backlight and frontlight maycomprise IR sources. In yet other touch panel systems, there is nobacklight and the frontlight comprises both IR sources and visible lightsources.

FIG. 2C illustrates a cross section of yet another exemplary touch panelsystem. A touch panel system 270 comprises a touch panel 272 having IRsensors 204 integrated therein. Touch panel system 270 does not comprisea frontlight or a backlight. Touch panel 272 also has IR sources 278integrated therein which are configured to illuminate objects abovetouchable surface 206 with IR radiation through touchable surface 206,as indicated by arrows 220.

Touch panel 272 may comprise a display that is configured to displayimages that are viewable via a touchable surface 276. Eye 215 indicatesa possible direction from which the images are viewed. The display maybe any suitable display in which IR sensors and IR sources can beintegrated.

For example, touch panel 272 may comprise an OLED display whichcomprises IR OLED emitters. Near-IR OLED emitters have beendemonstrated. Similarly, IR-sensitive organic photosensors are alsopossible, for example, by using a reverse-biased OLED.

In some touch panel systems, the touch panel may not comprise a display.Even if the touch panel comprises one or more components or elements ofa display, the touch panel may be configured as to not display anyimages. For example, this may be the case when the input tablet isseparate from the display. Other examples include a touchpad, a gesturepad, and similar non-display devices and components.

For some applications, it may be desirable to detect an object only ifit is in actual contact with the touchable surface of the touch panelsystem. The IR source of the touch panel system may be turned on only ifthe touchable surface is touched. Alternatively, the IR source may beturned on regardless of whether the touchable surface is touched, anddetection of whether actual contact between the touchable surface andthe object occurred is processed along with the output of the IR sensor.Actual contact between the touchable surface and the object may bedetected by any suitable means, including, for example, by a vibrationsensor or microphone coupled to the touch panel. A non-exhaustive listof examples for sensors to detect contact includes pressure-basedmechanisms, micro-machined accelerometers, piezoelectric devices,capacitive sensors, resistive sensors, inductive sensors, laservibrometers, and LED vibrometers.

IR sensors 204 may comprise suitable infrared-sensitive semiconductorelements. A non-exhaustive list of examples of semiconductor materialthat is infrared-sensitive includes polycrystalline silicon,monocrystalline silicon, microcrystalline silicon, nanocrystallinesilicon, plastic semiconductors and other non-silicon basedsemiconductors. Devices based on polycrystalline, microcrystalline,monocrystalline or nanocrystalline silicon may have better stabilitythan amorphous silicon devices. TFTs based on polycrystalline,microcrystalline, monocrystalline or nanocrystalline silicon may havehigher field mobility than amorphous silicon TFTs.

FIG. 3 illustrates a cross-section of an exemplary touch panel systemhaving an exemplary LCD incorporated therein. A touch panel system 300comprises a liquid crystal display 302 and a backlight 304. Backlight304 comprises arrays of light-emitting diodes (LEDs). In a colorbacklight, red LEDs 306, green LEDs 308 and blue LEDs 310 may be used.Liquid crystal display 302 typically comprises a diffuser 312 todisperse the light from backlight 304 and obtain a more uniformintensity over the surface of the display.

LCD 302 comprises a pair of polarizers 314 and 316 separated by a pairof glass substrates 318 and 320, which in turn are separated by a layerof liquid crystal material 322 contained in a cell gap betweensubstrates 318 and 320. In other implementations, substrates 318 and 320may be constructed from another transparent material, for example,plastic. Color filters, for example, a blue color filter (CF) 324 and ared color filter 326, are adjacent the inner surface of substrate 320.Each color filter transmits only part of the visible spectrum.

In the example shown in FIG. 3, LCD 102 is an active matrix LCD. Acontinuous electrode 328, termed “common electrode”, is located betweenthe color filters and liquid crystal material 322. Electrode 328 isconstructed using any suitable transparent electrode material, forexample, indium tin oxide (ITO). Individual pixel electrodes 330 may bepatterned from any suitable transparent electrode material, for example,ITO, and located on the inner surface of substrate 318.

As is known in the art, each pixel in an LCD is a small capacitor with alayer of insulating liquid crystal between two transparent electrodes.By applying a voltage to the pixel, one can control the intensity of thevisible light that is transmitted through LCD 302. In a color LCD, adisplayed pixel is formed of a plurality of sub-pixels. Different pixelarrangements are possible and not every pixel necessarily includessub-pixels of all three primary colors (typically, red, green and blue).For example, pixel arrangements that have on average two sub-pixels perdisplayed pixel are known. In another example, pixel arrangements thatinclude red, green, blue and white sub-pixels are known. By varying theintensity of transmitted light for each of a plurality of mono-colorsub-pixels that make up a displayed pixel, a color image is generated onthe surface of LCD display.

In a TFT active matrix LCD, substrate 318 includes TFTs which act asindividual switches for each pixel electrode 330 (or group of pixelelectrodes) corresponding to a pixel (or a group of pixels). The TFTsare described in further detail below with respect to FIG. 6. Pixelelectrodes 330, the TFTs, and substrate 318 form a backplane 332 of LCD302.

It is known, although not widely, that polarizers and color filters losetheir function in the near infrared (IR) region of the spectrum. A sheetpolarizer no longer polarizes electromagnetic waves at wavelengthslarger than about 800 to 850 nm. Red, green and blue pigment colorfilters, typically used in LCDs, also transmit most of the wavelengthsin the near infrared region of the spectrum. Hence, some near infraredlight is transmitted through a conventional LCD, independent of theimage displayed on the LCD display screen. For example, 40% of the nearinfrared light incident on one surface (front or back) of a conventionalLCD may be transmitted through the LCD. The precise percentage of nearinfrared light transmitted through a particular LCD may depend onseveral factors, including, for example, the pixel aperture ratio andinternal reflections in the cell.

LCD 302 comprises an IR sensor 334 integrated therein. As shown in FIG.3, IR sensor 334 is integrated into backplane 332. Any IR lightreflected from an object 336 in contact with or adjacent a touchablesurface 337 of LCD 302 will be transmitted through polarizer 316,substrate 320, common electrode 328, liquid crystal material 322 anddetected by IR sensor 334. An arrow 338 indicates the IR light reflectedfrom object 336 and an arrow 340 indicates the IR light in liquidcrystal material 322, the IR light possibly attenuated by polarizer 316,substrate 320, and common electrode 328.

IR sensor 334 may include, for example, a polycrystalline silicon TFT orphotodiodes, a monocrystalline silicon TFT or photodiode, amicrocrystalline silicon TFT or photodiode, or a nanocrystalline siliconTFT or photodiode. Infrared-sensitive semiconductor materials that arenot based in silicon are also contemplated for elements of IR sensor334.

In order to block visible light from reaching IR sensor 334, anIR-transmitting and visible-light absorbing filter may be integrated inLCD 302 opposite IR sensor 334. If such a filter is integrated in LCD302, the susceptibility of the IR sensor to noise from ambient lighting342, may be reduced. In the example shown in FIG. 3, the filter is anIR-transmitting polymer black matrix 344. Briefly, FIG. 4 illustrates anexemplary touch panel system 400 comprising an LCD 402. System 400differs from system 300 of FIG. 3 in that the filter is comprised of twocomplementary color filters that are overlapping, for example, bluecolor filter 324 and red color filter 326. This implementation relies onthe typical characteristics of visible light filters used in LCDs asoutlined above.

Returning to FIG. 3, backlight 304 comprises an IR source, which in thisexample is an IR LED 346. IR LEDs are commercially available at a lowcost at a range of wavelengths, including, for example, peak emissionwavelengths around 900 nm: 850 nm, 860 nm, 870 nm, 880 nm, 890 nm, 935nm, 940 nm and 950 nm. At some of these wavelengths, high power versionsof the IR LEDs are available.

Infrared radiation from the IR source, indicated by an arrow 348, istransmitted through LCD 302 after being diffused by diffuser 312, ifpresent. Some of the infrared radiation transmitted through LCD 304 isreflected off object 336 and detected by IR sensor 334 as describedabove.

FIG. 5 illustrates a cross-section of an exemplary touch panel systemhaving yet another exemplary liquid crystal display incorporatedtherein. A touch panel system 500 differs from system 300 of FIG. 3 inthat its backlight 504 does not comprise an IR source. Rather, system500 comprises an inverted frontlight 506 external to an outer surface ofpolarizer 316. Frontlight 506 comprises an infrared light guide 508 andan IR source coupled to light guide 508. In this example, the IR sourceis an IR LED 510 positioned to the side of light guide 508. Frontlight506 is described as “inverted” because the IR radiation from the IRsource is directed away from LCD 302, as indicated by arrows 512 and514. Alternatively IR source may emit polarized IR radiation andpolarization filters and/or reflectors blocking that polarization may beused between frontlight 506 and LCD 302. IR light reflected off object336 is not polarized, will pass through the polarization filters and/orreflectors, and be detected by IR sensor 334. Although system 500 isshown comprising IR-transmitting polymer black matrix 344, in alternateembodiments the system may include a filter comprised of twocomplementary color filters that are overlapping, for example, bluecolor filter 324 and red color filter 326.

The touch panel systems illustrated in FIGS. 3, 4 and 5 comprise LCDswith active matrix backplanes. In other embodiments, the touch panelsystem could comprise an LCD with an active matrix frontplane, a passivematrix backplane or a passive matrix frontplane.

The touch panel systems illustrated in FIGS. 3, 4 and 5 comprise LCDswith an IR-transmitting and visible-light absorbing filter between thetouchable surface of the system and the IR sensor. In other embodiments,the LCD may lack such a filter.

FIG. 6 illustrates an active matrix circuit having a TFT-based infraredsensor integrated therein. As is known in the art, an active matrixlayer comprises a set of data lines 600 and a set of select lines 602.An array of conductive lines may be created by including one data linefor each column of pixels across the display and one select line foreach row of pixels down the display. For each pixel, the active matrixlayer also comprises a pixel TFT 604 capacitively coupled to a commonline 606 through a capacitor 608. The source of pixel TFT 604 is coupledto its respective data line 600 and the drain of pixel TFT 604 iscoupled to its respective select line 602. To load the data to therespective pixels indicating which pixels should be illuminated,normally in a row-by-row manner, a set of voltages are imposed on therespective data lines 600 which imposes a voltage on the sources ofpixel TFTs 604. The selection of a respective select line 602,interconnected to the gates of pixels TFTs 604, permits the voltageimposed on the sources to be passed to drains of the pixel TFTs 604. Thedrains of the pixel TFTs are electrically connected to respective pixelelectrodes. In addition, a respective capacitance exists between thepixel electrodes enclosing the liquid crystal material, noted ascapacitances 609. Common line 606 provides a voltage reference. In otherwords, the voltage data (representative of the image to be displayed) isloaded into the data lines for a row of pixel TFTs 604 and imposing avoltage on select line 602 latches that data into the holding capacitorsand hence the pixel electrodes.

To integrate an IR sensor into the liquid crystal circuit, the activematrix layer also comprises an infrared-sensitive TFT 610 interconnectedto a readout TFT 612. The gate of readout TFT 612 may be interconnectedto select line 602, and the drain and the gate of infrared-sensitive TFT610 may be interconnected to a photobias line 614. (In otherimplementations, photobias line 614 and common line 606 may be one andthe same.) The source of readout TFT 612 may be interconnected to areadout line 616. A capacitor 617 may interconnect photobias line 614 tothe transistors. Readout line 616 is coupled to an operational amplifier618 connected to a reference voltage. The TFTs may be addressed by a setof multiplexed electrodes running along the gaps between the pixelelectrodes. Alternatively, the pixel electrodes may be on a differentlayer from the TFTs.

When a voltage is imposed on select line 602, this causes the voltage onreadout line 616 to be coupled to the drain of infrared-sensitive TFT610 and the drain of readout TFT 612, which results in a voltagepotential across capacitor 617. The state of infrared-sensitive TFT 610(“on” or “off”) will depend on whether IR radiation is incident oninfrared-sensitive TFT 610. For example, when a person touches thepanel, the IR reflection off the finger (about 10%) will turn theinfrared-sensitive TFT 610 partially “on”. If infrared-sensitive TFT 610is “off”, the voltage imposed across capacitor 617 will notsignificantly discharge through infrared-sensitive TFT 610, andaccordingly, the charge stored in capacitor 617 will be substantiallyunchanged. If infrared-sensitive TFT 610 is “on”, the voltage imposedacross capacitor 617 will significantly discharge throughinfrared-sensitive TFT 610, and accordingly, the charge stored incapacitor 617 will be substantially changed. To determine how muchcharge has leaked from capacitor 617, a voltage is imposed on selectline 602. This turns on readout TFT 612 and a charge flows throughreadout line 616 to reset the charge on capacitor 617. The outputvoltage of operational amplifier 618 is proportional or otherwiseassociated with the charge needed to reset the voltage on capacitor 617and is therefore a measure of the amount of IR radiation incident oninfrared-sensitive TFT 610 during the preceding frame time. This outputmay be processed along with the output from other IR sensors in thecircuit to identify a detected infrared image.

Infrared-sensitive TFT 610 and readout TFT 612, and the rest of thetransistors in the active matrix layer, may comprise any suitablesemiconductor material that is sensitive to infrared radiation,including polycrystalline silicon, monocrystalline silicon,microcrystalline silicon, nanocrystalline silicon, a plasticsemiconductor material, and semiconductor materials that are notsilicon-based.

For example, a microcrystalline silicon phototransistor can bemanufactured with Plasma chemical vapor deposition (CVD) equipment onthe same line as amorphous silicon TFTs. A large installed capacity isavailable for manufacturing a-Si TFT LCDs.

FIG. 7 is an example of a cross section of a bottom gateinfrared-sensitive TFT. A bottom gate infrared-sensitive TFT 700comprises a film 702 of semiconductor material, having a thickness d, asource 704, and a drain 706. TFT 700 also comprises a gate 708,deposited on a substrate such as a glass substrate 710. Techniques formanufacturing TFT 700 are well known in the art. Some of infraredradiation 712 incident on semiconductor film 702 is absorbed by film702. If gate 708 comprises a metal, for example, aluminum, that isreflective to infrared radiation, then at least some of infraredradiation 714 which is reflected from gate 708 is absorbed by film 702.

Ignoring optical interference, the absorption versus film thickness of asilicon-based TFT may be calculated using the following formula:A=(1−R)·(1−exp(−α(λ)·d)),  (1)where R is silicon film reflectance, α(λ) is the absorption coefficient,which is dependent on the wavelength λ, and d is the film thickness.

The absorption in percentage is calculated from this formula at λ=0.82nm and λ=0.94 nm for microcrystalline silicon (μc−Si) films of 200 nmthickness and 300 nm thickness. For comparison, the calculatedabsorption is compared to that of amorphous silicon (a-Si) films of thesame thicknesses. In these calculations, it was assumed that R=0. Theresults of these calculations are provided in the following table.

Absorption Absorption λ = 0.82 nm λ = 0.94 nm Film Thickness single-passsingle-pass 200 nm a-Si 0.04% 0.01% 300 nm a-Si 0.06% 0.02% 200 nm μc-Si 4.0%  1.4% 300 nm μc-Si  5.8%  2.1%It is apparent from this table that a photo TF with microcrystallinesilicon will absorb about 100 times as much near IR radiation as anamorphous silicon TFT with the same silicon film thickness.

As mentioned above, the gate of a TFT-based IR sensor may comprise ametal, for example, aluminum, that is reflective to infrared radiation.This may increase the effective optical path length to up to twice thefilm thickness d, depending on how much of the IR radiation isreflected. The absorption in percentage is calculated from the formulaabove at λ=0.82 nm and λ=0.94 nm for microcrystalline silicon (μc−Si)films of 200 nm thickness and 300 nm thickness, for a double pass of theIR radiation. In these calculations, it was assumed that R=0 and thatthe reflection from the gate metal is 100%. The results of thesecalculations are provided in the following table.

Absorption Absorption λ = 0.82 nm λ = 0.94 nm Film Thickness double-passdouble-pass 200 nm a-Si 0.08% 0.02% 300 nm a-Si 0.12% 0.04% 200 nm μc-Si 7.7%  2.8% 300 nm μc-Si 11.3%  4.2%The doubling of the optical path significantly increases the totalabsorption in the file. If interference is taken into account, the filmthickness may be further optimized to operate on an interference maximumfor the absorption at the chosen wavelength. The photocurrent in thefilm is proportional to the absorption, assuming each absorbed photoncontributes to the photocurrent.

FIG. 8 illustrates an active matrix circuit having a photodiode-basedinfrared sensor integrated therein. The circuit of FIG. 8 differs fromthat of FIG. 6 in that an infrared-sensitive photodiode 800 replacesinfrared-sensitive TFT 610. Photodiode 800 is interconnected to readoutTFT 612. The anode of photodiode 800 may be interconnected to photobiasline 614, and the cathode of photodiode 800 may be interconnected to thedrain of readout TFT 612. For example, photodiode 800 may be a lateralPIN diode of polycrystalline silicon, and can be manufactured with astandard Low Temperature Poly Silicon Complementary Metal-OxideSemiconductor (CMOS) process, which is common in the active matrix LCDindustry.

FIG. 9 illustrates a cross-section of an exemplary touch panel system900 having an organic light emitting diode (OLED) display incorporatedtherein. Sandwiched between a cover glass 902 and a glass substrate 904is an OLED 906. A translucent cathode 908 is embedded in cover glass902, and a metal anode 910 couples OLED 906 to a drive TFT 912. DriveTFT 912 and an address TFT 914 are comprised in an active matrixbackplane 916. Visible light radiating from OLED 906, indicated by anarrow 918, is directed outward through cover glass 902. IR sensors maybe integrated into active matrix backplane 916, for example, asdescribed below with respect to FIGS. 11 and 12. Alternatively, asdescribed above with respect to FIG. 2C, OLED 906 may compriseIR-sensitive organic photosensors. A backlight (not shown) or afrontlight (not shown) may comprise IR sources (not shown).Alternatively, as described above with respect to FIG. 2C, OLED 906 maycomprise IR OLED emitters. IR radiation from the IR sources may beincident on an object 936 above a touchable surface of touch panelsystem 900. IR radiation reflected from the object, as indicated by anarrow 938, may be detected by the IR sensors.

FIG. 10 illustrates a cross-section of another exemplary touch panelsystem 1000 having an OLED display incorporated therein. An OLED 1006 issandwiched between a metal cathode 1010 and a transparent anode 1008. Anactive matrix layer 1016 comprises a drive TFT 1012 and an address TFT1014. Drive TFT 1012 is coupled to transparent anode 1008. Visible lightradiating from OLED 1006, indicated by an arrow 1018, is directedtowards a glass substrate 1004. IR sensors may be integrated into activematrix backplane 1016, for example, as described below with respect toFIGS. 11 and 12. Alternatively, as described above with respect to FIG.2C, OLED 906 may comprise IR-sensitive organic photosensors. A backlight(not shown) or a frontlight (not shown) may comprise IR sources (notshown). Alternatively, as described above with respect to FIG. 2C, OLED1006 may comprise IR OLED emitters. IR radiation from the IR sources maybe incident on an object 1036 above a touchable surface 1005 of touchpanel system 1000. IR radiation reflected from the object, as indicatedby an arrow 1038, may be detected by the IR sensors.

FIG. 11 illustrates an exemplary active matrix OLED circuit 1100 havinga TFT-based infrared sensor integrated therein. Circuit 1100 comprisespixel circuits 1102 having two TFTs per pixel: a drive TFT 1104 and anaccess TFT 1106. Each pixel circuit 1102 also comprises a storagecapacitor 1108 and an OLED 1110 coupled to a common OLED electrode 1112.

The active matrix layer comprises a set of data lines 1114 and a set ofselect lines 1116. The source of access TFT 1106 is coupled to itsrespective data line 1114 and the drain of access TFT 1106 is coupled toits respective select line 1116. Access TFT 1106 is capacitively coupledto a common bias line 1118 through storage capacitor 1108.

There are many other variations of pixel circuits having two or moreTFTs per pixel.

To integrate an IR sensor into the active matrix OLED circuit, theactive matrix layer also comprises an infrared-sensitive TFT 1120interconnected to a readout TFT 1122. The gate of readout TFT 1122 maybe interconnected to select line 1116, and the drain and the gate ofinfrared-sensitive TFT 1120 may be interconnected to common bias line1118. The source of readout TFT 1122 may be interconnected to a readoutline 1124. A capacitor 1126 may interconnect common bias line 1118 tothe transistors. Readout line 1124 is coupled to an operationalamplifier 1128 connected to a reference voltage. The TFTs may beaddressed by a set of multiplexed electrodes running along the gapsbetween the pixel electrodes. Alternatively, the pixel electrodes may beon a different layer from the TFTs.

When a voltage is imposed on select line 1116, this causes the voltageon readout line 1124 to be coupled to the drain of infrared-sensitiveTFT 1120 and the drain of readout TFT 1122, which results in a voltagepotential across capacitor 1126. The state of infrared-sensitive TFT1120 (“on” or “off”) will depend on whether IR radiation is incident oninfrared-sensitive TFT 1120. For example, when a person touches thepanel, the IR reflection off the finger (about 10%) will turn theinfrared-sensitive TFT 1120 partially “on”. If infrared-sensitive TFT1120 is “off”, the voltage imposed across capacitor 1126 will notsignificantly discharge through infrared-sensitive TFT 1120, andaccordingly, the charge stored in capacitor 1126 will be substantiallyunchanged. If infrared-sensitive TFT 1120 is “on”, the voltage imposedacross capacitor 1126 will significantly discharge throughinfrared-sensitive TFT 1120, and accordingly, the charge stored incapacitor 1126 will be substantially changed. To determine how muchcharge has leaked from capacitor 1126, a voltage is imposed on selectline 1116. This turns on readout TFT 1122 and a charge flows throughreadout line 1124 to reset the charge on capacitor 1126. The outputvoltage of operational amplifier 1128 is proportional or otherwiseassociated with the charge needed to reset the voltage on capacitor 1126and is therefore a measure of the amount of IR radiation incident oninfrared-sensitive TFT 1120 during the preceding frame time. This outputmay be processed along with the output from other IR sensors in thecircuit to identify a detected infrared image.

FIG. 12 illustrates an exemplary active matrix OLED circuit 1200 havinga photodiode-based infrared sensor integrated therein. Circuit 1200differs from circuit 1100 in that an infrared-sensitive photodiode 1202replaces infrared-sensitive TFT 1120.

The IR sensors in a touch panel system according to the describedtechnology will also be sensitive to IR in the ambient radiation. Roomlight from incandescent lamps has a significant IR component. Likewise,in outdoor conditions, the solar spectrum at different times of the dayincludes IR radiation. It is known that the solar spectrum has a dip atabout 920 nm. Therefore, IR sources emitting a peak wavelength at ornear 920 nm may be used.

To improve signal-to-noise ratio in a touch panel system according tothe described technology, the IR source may be pulsed in synchronizationwith the detection by the IR sensor. For example, for a sensor thatintegrates the signal during the frame time, the IR source(s) may be“on” during the odd frames and “off” during the even frames. Thisrequires vertical scanning of the array of IR LEDs in the addressingdirection of the rows. The differential signal between odd frames andeven frames may cancel out the direct current (DC) noise from an IRbackground.

The signal-to-noise ratio may also be improved by increasing theintensity of the IR source.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A touch panel system comprising: a touchablesurface; a backlight including visible light sources and at least oneinfrared source, wherein the at least one infrared source is configuredto direct infrared radiation through the touchable surface forilluminating objects that are in contact with or adjacent to thetouchable surface with infrared radiation; a touch panel displayconfigured to illuminate pixels for visibly displaying an image, thetouch panel display comprising: a matrix circuit including pixel circuitelements; and infrared sensors that are integrated in the matrix circuitwith the pixel circuit elements and distributed parallel to thetouchable surface, wherein: the infrared sensors are configured todetect reflected infrared radiation incident on the infrared sensors,infrared radiation directed by the at least one infrared source throughthe touchable surface is not detected by the infrared sensors, and theinfrared sensors are shielded from visible light emitted by the visiblelight sources and visible light radiated by the pixels via filterslocated between the touchable surface and each of the infrared sensors;and a computing device coupled to the touch panel display for processingreflected infrared radiation detected by the infrared sensors, whereinthe computing device is configured to: cause a multi-player game to bedisplayed by the touch panel display, process reflected infraredradiation detected by the infrared sensors that is directed through thetouchable surface by different physical game pieces which are in contactwith the touchable surface and which are associated with differentplayers of the multi-player game, identify and distinguish between thedifferent physical game pieces, detect locations of the differentphysical game pieces, and alter display of the multi-player game basedon the locations of the different physical game pieces.
 2. The touchpanel system of claim 1, wherein: the reflected infrared radiationdetected by the infrared sensors is processed to identify anddistinguish between the different physical game pieces by shape.
 3. Thetouch panel system of claim 1, wherein: the computing device identifiesand distinguishes the different physical game pieces based on symbols orcodes imprinted on the different physical game pieces.
 4. The touchpanel system of claim 1, wherein the touch panel display is a liquidcrystal display.
 5. The touch panel system of claim 4, wherein theliquid crystal display comprises one of an active matrix backplane, anactive matrix frontplane, a passive matrix backplane, and a passivematrix frontplane.
 6. The touch panel system of claim 1, wherein thetouch panel display is an organic light emitting diode display.
 7. Thetouch panel system of claim 6, wherein the at least one infrared sourceis an organic light emitting diode.
 8. The touch panel system of claim6, wherein the infrared sensors comprise organic photosensors.
 9. Thetouch panel system of claim 1, wherein the infrared sensors comprisethin film transistors.
 10. The touch panel system of claim 1, whereinthe infrared sensors comprise photodiodes.
 11. A touch panel displaycomprising: a touchable surface; a plurality of pixels for visiblydisplaying an image on the touchable surface; a color backlightcomprising a plurality of color light sources for emitting visiblelight; at least one infrared source configured to direct infraredradiation through the touchable surface for illuminating one or moreobjects that are in contact with or adjacent to the touchable surfacewith infrared radiation; a backplane including pixel circuit elements;infrared sensors that are integrated in the backplane with the pixelcircuit elements and distributed parallel to the touchable surface,wherein: the infrared sensors are configured to detect reflectedinfrared radiation incident on the infrared sensors, infrared radiationdirected by the at least one infrared source through the touchablesurface is not detected by the infrared sensors, and the infraredsensors are shielded from visible light emitted by the color lightsources and visible light radiated by the pixels via filters locatedbetween the touchable surface and each of the infrared sensors; and acomputing device for processing reflected infrared radiation detected bythe infrared sensors, wherein the computing device is configured to:cause a game to be displayed on the touchable surface, process reflectedinfrared radiation detected by the infrared sensors that is directedthrough the touchable surface by different physical game pieces whichare in contact with the touchable surface, identify the differentphysical game pieces based on symbols or codes imprinted on thedifferent physical game pieces, and alter display of the game on thetouchable surface.
 12. The touch panel display of claim 11, wherein thetouchable surface is implemented by a liquid crystal display.
 13. Thetouch panel display of claim 11, wherein the touchable surface isimplemented by an organic light emitting diode display.
 14. The touchpanel display of claim 13, wherein the infrared sensors comprise organicphotosensors.
 15. The touch panel display of claim 11, wherein theinfrared sensors comprise thin film transistors.
 16. The touch paneldisplay of claim 11, wherein the infrared sensors comprise photodiodes.17. The touch panel display of claim 11, wherein the computing devicecauses a video clip to be displayed on the touchable surface in responseto positioning a physical game piece at a certain location on thetouchable surface.
 18. A method performed in a touch panel system, themethod comprising: emitting visible light from a backlight of the touchpanel system; visibly displaying a game on a touchable surface of atouch panel display by illuminating pixels of the touch panel display;directing infrared radiation from at least one infrared sourceintegrated in the touch panel system through the touchable surface forilluminating different physical game pieces that are in contact with thetouchable surface with infrared radiation; detecting reflected infraredradiation incident on infrared sensors which are integrated in the touchpanel display with pixel circuit elements and distributed parallel tothe touchable surface, wherein: infrared radiation directed by the atleast one infrared source through the touchable surface is not detectedby the infrared sensors, and the infrared sensors are shielded fromvisible light emitted by the backlight and visible light radiated by thepixels via filters located between the touchable surface and each of theinfrared sensors; and processing reflected infrared radiation that isdirected through the touchable surface by the different physical gamepieces and detected by the infrared sensors to: identify the differentphysical game pieces based on symbols or codes imprinted on thedifferent physical game pieces, and alter display of the game on thetouchable surface of the touch panel display.
 19. The method of claim18, wherein: the different physical game pieces are associated withdifferent players of a multi-player game.
 20. The method of claim 18,wherein a video clip is displayed on the touchable surface in responseto positioning a physical game piece at a certain location on thetouchable surface.